Newcomen Atmospheric Engine Description
The engine photos on this page were taken of engines exhibited at the Henry Ford Museum in Dearborn, MI.
This Newcomen engine in Figure 1 is from approx. 1760. It is the oldest Newcomen engine in existence. The person in the photo gives you some idea of the scale! Note the large wooden beam and support structure. The original Newcomen engine (1712) was more primitive than then engine shown here.
Figure 2 shows the steam piston, the boiler, steam line, and feed water line. The feed water line passes through a tank before dropping to the boiler. This permits any air bubbles entrained in the feed water line to exit before the water enters into the boiler.
This engine incorporates some improvements relative to the earliest Newcomen engines. In Newcomen's original implementation, the boiler was placed directly under the steam piston, and the steam piston needed to be mounted relatively high. Building a rigid structure high off the ground that could take the tremendous pounding of the steam cylinder was difficult. Later pumps used the separate boiler shown here and the piston could be placed closer to the ground. Published descriptions of Newcomen pumps include illustrations showing the pump protected by a roof built from the center of the main beam over the steam cylinder and boiler. This auxiliary roof construction was also simplified by placing the steam piston near the ground.
Description of Operation
The original pumps were designed to lift water on the upward stroke. The pumps are called air pumps because the lifting action permitted them to pump air as well as water. The designs for alternate pump configurations are described on the pump page, as well as a description of the check valves D-J which operated automatically to prevent backflow.
Step 1 - upward stroke of steam piston (upward on left side).
Valves A, D, E, are open, and valve B, C, F-J are closed. Weight of the pump side pulls beam down on the right lowering the pistons in the main and auxilary pumps. (On some engines extra weight is added to the pump side of the beam to assure it is heavier than the steam side). This action pulls up the steam piston, and steam flows into the cylinder. Note that the steam piston is attached by a chain - it can't push up the beam! The boiler operates at nearly atmospheric pressure. During this upward motion, steam piston condensate flows into the condensate pump and lifted to the water reservoir.
The valves F-J in the main and auxilary pumps are closed during this step. The pistons pass downward through the liquid, permitting the water to pass from below the piston to above the piston as described on the pump page.
Step 2 - downward stroke of steam piston (downward on left side).
Valve A, D, E are closed, valves B, C, F-J are opened. Water is sprayed into the cylinder below the piston to condense the steam, creating a vacuum inside. The atmospheric pressure on the outside pushes the piston downwards. This action pulls down the beam and fills the main water pump and auxiliary pumps and lifts the water above the pistons. The top of the steam cylinder is open and the steam piston is visible from the top. Water is sprayed onto the top of the piston via valve C to maintain a good seal. Even though Newcomen was a blacksmith, he couldn't make perfectly round cylinders in those days. The cylinders were typically cast and slightly out of round, as well as the pistons! The seal was made by a packing of oakum (hemp fibers soaked in tar) that was jammed in a channel between the piston and cylinder and held in place by weights. Newcomen found it necessary to keep the seal wet in order to maintain the vacuum.
Early Newcomen engines simply drained the condensate water from the steam piston. In the engine illustrated here, a condensate pump is provided that sits in a well that would have been filled with water, presumably pumped from the mine by the main pump. This particular Newcomen engine also has an auxiliary pump to provide condensing water. The internal portion of the water reservoir at the top of the beam support isn't visible from the ground level at the museum, but it probably has separate reservoirs for the hot condensate that returns to the boiler and for the cold condensing water.
Thank you for your interest!
© 2001-13, Carl T. Lira, firstname.lastname@example.org
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Prepared as a supplement to Introductory Chemical Engineering Thermodynamics.